1. Field of the Invention
The present invention relates generally to a high frequency circuit integrated-type antenna component used as an antenna for communication.
Examples of the antenna component include an antenna integrated-type demultiplexer board in which an antenna element and a demultiplexer board are integrated with each other.
2. Description of Related Art
The current trend in the design of radio communication devices is to provide devices capable of coping with a plurality of different communication systems. In such a communication device, components for radio communication capable of transmitting and receiving a plurality of signals in different frequency bands which correspond to the different communication systems are required. In order to keep the entire communication device small and lightweight, it is required that each of the components is made multi-functional and is made small and lightweight.
An antenna is one of the largest components used for the radio communication device. One method of reducing the size of the antenna is to form a resonance-type antenna including an antenna element whose length is smaller than a wavelength and an impedance converter. An example of the antenna is a microstrip antenna. However, the antenna thus miniaturized are liable to have narrow band characteristics. Therefore, when the antenna is utilized for the radio communication device capable of coping with the plurality of systems, a plurality of antennas must be used. Even when an antenna in another form is used, the wider a frequency range to which the communication device should correspond is, the more difficult a single small-sized antenna which can be utilized is to find out.
In the radio communication device comprising individual antennas for a plurality of communication systems, a plurality of power feeding lines for respectively transmitting signals between the antennas and transmitters-receivers corresponding thereto are required. In order to make the communication device small and lightweight and reduce the cost thereof, it is desirable that the number of components is reduced by sharing the components. In feeding power to the antennas, it is desirable to use one power feeding line, if possible.
A circuit as shown in FIG. 20 or FIG. 21, for example, is used, in order to distribute a signal from a single transmission line, through which a plurality of signals having different frequencies are transmitted, into different transmission lines for the frequencies or to synthesize the plurality of signals having different frequencies, which have been received by the plurality of antennas, into a single transmission line.
In the circuit shown in FIG. 20, a signal from a single transmission line 81 through which a plurality of signals having different frequencies are transmitted is distributed into a plurality of transmission lines 82a, 82b, and 82c. Thereafter, the signals having the respective signal frequencies are selectively passed by filters 83a, 83b, 83c respectively adaptable to the signal frequencies, and are respectively transmitted to antenna elements 85a, 85b, and 85c via power feeding lines 84a, 84b, and 84c. 
In the circuit shown in FIG. 21, a single transmission line 86 through which a plurality of signals having different frequencies are transmitted is connected to a demultiplexer 87. A signal from the transmission line 86 is branched for the different frequencies by the demultiplexer 87, and signals obtained by the branching are respectively transmitted to antenna elements 89a, 89b, and 89c via power feeding lines 88a, 88b, and 88c. 
In the circuit shown in FIG. 20, however, signal power is wasted because it is divided.
On the other hand, the circuit shown in FIG. 21 is advantageous in that signal power is not wasted. In an actual structure of the circuit shown in FIG. 21, however, the antenna elements 89a, 89b, and 89c and the demultiplexer 87 are separately formed and then electrically line-connected to each other. In a case where the power is fed to a plurality of antennas via a demultiplexer from one power feeding line, however, if the power feeding line between the demultiplexer and the antenna is long, the loss of the signal power is increased.
On the other hand, it is also proposed that the demultiplexer and the antenna are formed on a surface of a dielectric board. Because the demultiplexer and the antenna are provided within the same plane, the power feeding line can be shortened. However, the dielectric board is required to have an area corresponding to both the antenna and the demultiplexer, which is unfavorable for miniaturization. If the demultiplexer is brought too close to the antenna, the antenna and the demultiplexer interfere with each other, which may degrade characteristics.
An object of the present invention is to provide a high frequency circuit integrated-type antenna component which can be miniaturized by integrally forming an antenna and a high frequency circuit (a stacked circuit section) such as a demultiplexer.
Another object of the present invention is to provide an antenna integrated-type demultiplexer board capable of preventing an antenna and a demultiplexer from interfering with each other.
Still another object of the present invention is to provide a chip antenna component having a high degree of freedom in design.
The inventors have found out that the above-mentioned objects are achieved by integrally forming an antenna element and a demultiplexer board provided with a demultiplexing circuit as well as forming a grounding layer between the antenna element and the demultiplexing circuit as a result of making various considerations in order to solve the above-mentioned problems in the prior art.
The inventors have found out that the same object is achieved by arranging, where an antenna element is a slot antenna, a slot on a grounding layer formed on a surface or in an inner part, where the demultiplexing circuit is not provided, of the demultiplexer board such that signal transmission to the demultiplexing circuit is allowed.
Specifically, the antenna integrated-type demultiplexer board according to the present invention is constructed by forming a demultiplexing circuit (an example of a high frequency circuit) on a surface or in an inner part of a dielectric board, forming a grounding layer on a surface, where the demultiplexing circuit is not provided, of the dielectric board, forming an antenna element in the grounding layer or disposing the antenna element on the grounding layer, and connecting the antenna element and the demultiplexing circuit such that signal transmission is allowed.
In the above-mentioned construction, it is desirable that the demultiplexing circuit comprises a directional filtering circuit comprising a directional coupling circuit and a ring-type resonance circuit. Further, it is desirable that the demultiplexing circuit comprises a plurality of directional filtering circuits which differ in operation frequencies in order to correspond to a plurality of different frequencies to be used, and the plurality of directional filtering circuits are arranged in descending order of the operation frequencies from the side of power feeding.
A slot antenna is suitable for the antenna element in the grounding layer. It is desirable that signal transmission is made by electromagnetically coupling the antenna element to the demultiplexing circuit. Further, a plane-type antenna such as a microstrip antenna, or a dielectric resonator antenna is suitable as the antenna element disposed on the grounding layer. It is desirable that the signal transmission is made to the demultiplexing circuit by providing a through conductor penetrating through the dielectric board from the demultiplexing circuit and extending into the dielectric resonator antenna and connecting the through conductor to the demultiplexing circuit.
An antenna board provided with the antenna element on a dielectric board may integrally mounted on the demultiplexer board.
In this case, a grounding layer may be provided on one of surfaces, a surface of the antenna board, or an antenna mounting surface of the demultiplexer board. Alternatively, the antenna board and the demultiplexer board may respectively comprise grounding layers, and the grounding layers may be electrically connected to each other.
In the antenna board, a plurality of antenna elements which differ in operation frequencies can be also provided on one of surfaces of the dielectric board. Further, a plurality of antenna boards respectively provided with the antenna elements which differ in the operation frequencies may be integrally mounted on a surface of the demultiplexer board.
A chip antenna component according to the present invention is constructed by integrally forming an antenna element and a stacked circuit section comprising at least one signal input terminal and two or more signal output terminals and connecting at least one of the signal output terminals to the antenna element.
According to the construction, it is possible to provide a small-sized chip antenna component which has a small mounting area, has a high degree of freedom in antenna arrangement, and is easily subject to change in design in feeding a signal having a plurality of frequencies to a plurality of antennas using one power feeding line or in forming an array antenna.
In the above-mentioned construction, it is desirable that a demultiplexing circuit and/or a multiplexer is formed in the stacked circuit section. It is desirable that the demultiplexing circuit and the multiplexer respectively comprise directional filtering circuits each comprising a directional coupling circuit and a ring-type resonance circuit. It is desirable that the antenna element is a plane-type antenna such as a microstrip antenna.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.